Referring to prior art examples shown in FIGS. 1-3B, lamps 900 such as a 1000 watt double ended horticultural lamp (1000 W DE), e.g., with a high pressure sodium (HPS) arc tube inside a “quartz” (fused silica) outer jacket, have a special “base” 920 (e.g., designated as a K12×30 s base) that interfaces with a corresponding fixture socket (see FIGS. 3A-3B) in order to hold the lamp in the fixture while also providing electrical connection to the lamp lead wires. The base 920 comprises an outer lead assembly 932 made from a stranded (a.k.a. “braided”) Ni wire (may be an alloy such as NiMn) 918 that is mechanically and electrically attached to a refractory metal (e.g., molybdenum (Mo) or Mo alloy) outer pinch lead wire 916 that extends out of a “pinch seal” 924 end of the quartz outer jacket 922 of the lamp 900.
As shown in FIGS. 3A-3B a typical fixture socket for this K12×30 s base 920 has a pair of flat faced contact plates to clamp the outer lead assembly 932 (should be only the stranded wire lead 918 part of the outer lead assembly 932). The socket clamping/contact plates are a fixed longitudinal distance apart, and registered against the pinch seal ends 924 to be a fixed distance away from each pinch 924 (which is why the pinch is considered part of the lamp base 920, along with the outer lead assembly 932). Regarding lamp installation in the fixture/sockets, keep in mind that the lamp 900 is typically pushed upward into an overhead fixture wherein the lamp hangs underneath the sockets. To install a lamp 900, the lamp body is held and used to push the lamp outer lead assemblies 934 into the “bottom” of the space between opened contact plates, holding the pinch seals 924 against stops in the socket, and sliding the sockets until they lock in a closed position where the contact plates are squeezed together to pinch the lead wire to make a mechanical and electrical connection. The contact plates are only located at the “bottom” of the gap, so if a lead assembly 934 is bent away from the bottom when inserted (e.g., by misalignment or by being dragged by some kind of interference), then the clamping plates may only partly contact the lead wire. Given the high current (e.g., 8 amps) supplying the lamp, and high starting voltages, a poor electrical connection can cause arcing and/or overheating leading to serious consequences.
The attachment/connection 932 in the outer lead assembly 934 between two generally round wires is difficult, especially because: they cannot be soldered due to high lamp operating temperature; and a mechanical/compression joint by itself (e.g., using a surrounding sleeve that is crushed around the overlapping ends) is not reliable due to cyclic thermal expansion and contraction of dissimilar metals and further due to surface oxidation developing over time. This connection is even more challenging because the wires are such different metals with different melting points, have different diameters (e.g., 1 mm solid vs. ˜1.5 mm twisted bundle), and different amounts of hardness/compressibility (stranded Ni is more easily deformed by compression, while solid Mo is relatively hard and non-compressible). Furthermore, the stranded wire has, for example, 19 strands that are twisted together like a cable, which makes resistance welding very difficult and inconsistent due to variable resistance between strands. Finally, as further detailed below, the connection 934 must be made after lamp sealing, so the outer pinch lead 116 will generally be oxidized so that it must be cleaned before a connection can be made.
The connection method that has been in use in the prior art is a combination of resistance spot welding of various portions of overlapping wire ends and a sleeve that is crimped around one or both of the overlapping wire ends. This prior art connection will be generically referenced herein as a “crimp connection” 932, even though welding is also typically involved. For example, the sleeve may be crimped around both wire ends to hold them together and the spot weld(s) are made simultaneously through all of the overlapping layers, or separately where the sleeve overlaps each wire. Or, for example, the sleeve may not surround the wires so that the spot welds can be made separately between each lead and the sleeve, thereby passing weld current through only one layer of the sleeve material. Before resistance welding, any oxidation must be cleaned off the wire surface(s), for example by brushing or sand blasting. The longitudinal positioning of the sleeved connection 934 is not precise enough to ensure adequate connection unless there is extra overlapping length (i.e., a larger target) in which the connection can be made. Therefor any solid wire 916 extending beyond the sleeve is usually trimmed off in an attempt to avoid potential interference with the socket clamp (see FIG. 1A).
Other techniques and method variations may be employed to establish the prior art electrical-mechanical connection designated herein as a crimp connection 932, however they all produce similar results as shown in FIGS. 2-3 by images of the assembly 934 from three different prior art lamp manufacturers. What the examples show is (a) offset misalignment of the Mo outer pinch lead 916 and the stranded Ni lead 918, (b) a stranded lead that is offset from the lamp axis in different directions (“crankshaft”—compare ends of the lamp in FIG. 2), (c) a stranded lead 918 that is typically not straight and may also extend outward at an angle to the outer pinch lead 916, and (d) an irregularly shaped larger diameter portion (a lump or bump) where the sleeve covers the connection 932. Any of these irregularities can cause serious electrical problems if it interferes with optimum closure of the socket clamps which need to compress and grip a significant length of the stranded lead.
FIGS. 1-3 show typical construction details and example images of prior art implementations of this base 920 in a 1000 W DE HPS horticultural lamp 900 as made and sold by three different lamp making companies. The lamp is a high power HID light source (e.g., HPS) sealed in a tubular quartz outer jacket 922, the quartz material being used to withstand the very high operating temperature imposed on the envelope of a lamp like this, which is a horizontal burning high wattage lamp with a close fitting outer jacket having a gas fill.
Also referring to FIGS. 1-2, for hermetically sealing a quartz envelope 922 around an electrical lead wire 916, a quartz pinch seal 924 is made (e.g., prefabricated) using a 3 part foliated lead assembly 910 wherein the inner pinch lead 912 and outer pinch lead 916 are solid wires (typically round) that are welded to the face of a thin foil 914, all made of refractory metal(s) such as some form of molybdenum (Mo). During the pinch sealing operation the 3 part foliated lead assembly 910 is held in position and the quartz tube end is heated enough for it to be pinched flat into a generally planar shape as shown.
Importantly, in the prior art the stranded wire lead can only be added (to complete the lamp “base”) after the pinch seal is completed. This is because the prior art crimp connection 932 between the Mo outer pinch lead and the Ni stranded wire will not survive the extreme heating it would receive during the quartz pinch sealing process (quartz/fused silica “glass” requires the most intense heat of all lampmaking glass materials, e.g., 2,000 C versus around 1500 C for hard glass). As a result of the heating in atmosphere, the outer pinch lead 916 develops an oxide layer that must be removed (e.g., by sand blasting, brushing, etc.) before an acceptable weld connection can be made. Further complicating matters, the heating causes partial recrystallization of the Mo wire, making it somewhat brittle, therefor the crimp connection process must take care to avoid breaking the Mo wire. (The recrystallization may be controlled by using doped moly.)
There are many disadvantages and potential problems with this prior art “crimp connection”, including one or more of the following:                Crimp connection can have a poor (high resistance) electrical connection of Ni to Mo because mixed materials overlapped and wrapped in sleeve do not make a good weld using a resistance welder.        Crimp connection can cause an insecure hold and/or poor (high resistance) electrical connection between the outer lead and the fixture socket due to irregularly shaped crimp connection, inconsistent location, and non-aligned offset wires. (The socket uses a pair of flat faced contact bars to clamp the Ni stranded wire lead at each end. The socket clamps are a fixed longitudinal distance apart so inaccurate crimp connection location can result in a socket clamping onto the crimp sleeve instead of the Ni stranded wire.)        Offset or otherwise misaligned outer leads may tilt the lamp off of the optimum axial location in the fixture reflector. Keeping the arc tube (which is mounted on center axis of the lamp) centered is important for the reflector because all DE reflectors are designed to efficiently reflect the light produced by the lamp based on the arc tube being positioned in the center of the reflector, otherwise this will change the optics and efficiency of the reflector, the fixture, and the overall lighting quality.        Crimp connection is a complicated process that is difficult to automate and is therefor time consuming/expensive.        Quality control issues include: length of connected outer lead, amount of overlap, location of overlap, non-zero angle between wires, and the like.        